Photo-conductive image intensifiers

ABSTRACT

Coupling conductors are disposed in electrical contact between the input photo-conductive layer and the output electroluminescent layer of a photo-conductive image intensifier panel so that the photo-conductive layer acts only to an extremely small depth of light penetration and therefore photo-current occurs mainly at the input surface of the photo-conductive layer and is then conducted directly to the electroluminescent layer, avoiding the severe attenuation of the photo-current when it must pass through the thickness of the photo-conductive layer.

United States Patent Harwood et al.

PHOTO-CONDUCTIVE IMAGE INTENSIFIERS Inventors: Mervyn Geoffrey- Harwood, Bromley; John Schofield, Coulsdon, both of England Assignee: Philips Corporation Filed: Dec. 7, 1970 Appl. No.: 95,437

Foreign Application Priority Data Dec. 11, 1969 Great Britain ..60,556/69 US. Cl. ..250/213, 313/108 R Int. Cl ..H0lj 31/50 Field of Search ..3l3/l08 A, 108 R; 250/213 References Cited UNITED STATES PATENTS 2/1966 Frankl ..3l3/l08 A X Evans ..250/2l3 R I [4 1 Oct. 17,1972

3,300,645 1/1967 Winslow ..3l3/l08 A X 3,405,276 10/1968 Szepesi ..250/2l3 R 3,590,253 6/1971 Novice et al. ..3l3/108 A X 3,604,938 9/1971 Kohashi.. ..3l3/l08 A X 3,558,974 1/1971 Stewart ..250/2l3 X Primary ExaminerJohn S. l-leyman Att0rney-Frank R. Trifari 57 ABSTRACT 8 Claims, 5 Drawing Figures PATENTEDucI 11 m2 SHEET 1 BF 3 (PR10R AR T) 1 G F 3 E INVENTORS MERVYN G. HARWOOD BY JDHN sc OFIELD AGEN a A E W ovvmlnnviii prises:

PHOTO-CONDUCTIVE IMAGE INTENSIFIERS This invention relates to photo-conductive image intensifiers of panel-type construction.

Such a construction has been proposed in US. Pat. No. 2,920,232 (l-IJ. Evans) which construction coma. a continuous photo-conductive (PC) input layer having its input face exposed to incoming light;

b. a square-meshinput electrode located against the output face of the said PC layer;

c. within each mesh .of said input electrode a coupling conductor which is insulated except for having its input end in contact with an area of the output face of the PC layer; g

d. a conductive plate electrically connected to the output end of each of said coupling conductors, all said plates being coplanar and spaced from each other;

, e. an electroluminescent (EL) layer in contact with the output faces of all of said plates; and

f. an output electrode in contact with the output face of said EL layer.

The coupling conductors are provided in this arrangement (and also in arrangements according to the invention) to couple the input or PC stage to the output or EL display stage of the device.

In the above known arrangement the PC layer, being continuous, extends over the input ends of the coupling conductors. Photo-conduction operates to some extent in the plane of the panel, i.e., between the input end of each coupling conductor and the corresponding mesh which surroundsit, and this is desirable since the PC layer acts effectively only to an extremely small depth of light penetration. However, this advantage is lost in the region of the coupling conductor since the photocurrent has to flow away from the active PC input surface and through the thickness of the PC layer in order to reach the underlying conductor, and the same occurs near the input electrode since the latter is on the output side of the PC layer.

The present invention is based in part on the realization that even a very small thickness of the PC layer can have a very damaging effect on the sensitivity and performance of the panel if inserted in the circuit path. Thus, for example, if the PC layer is of CdS having a thickness of only p, then with an attenuation to light b. an input electrode of grid form in contact with the input face of said PC layer at areas separated from said spaced apertures;

c. a coupling conductor corresponding to each spaced aperture of the PC layer'and having its input end located inside the aperture and in contact with the input face of saidPC layer at the periphery of the aperture; a

d. a conductive plate electrically connectedto the output end of'each of said conductors, all said plates being co-planar and spaced from each other;

e. an electroluminescent (EL) layer in contact with the output faces of all of said plates; transparent fia output electrode in contact. with the output face of said EL layer; and

g. said conductive plates being opaque to light emitted by said EL layer and/or'having as backing a filler which is opaque thereto. 1

The fact that the input electrode and coupling conductors are in contact with the input face of the PC layer (as opposed to its output face as in the Evans arrangement) permits the deviceto operate without the aforementioned harmful effects of the impedance of the PC layer. This reduction in the losses of the system obviates the need for optical feedback, and such feedback is prevented by ensuring sufficient opaqueness in the plates and/or any filling material that may be provided between the coupling conductors.

Preferably the plates reflect light from the EL layer in addition to being opaque thereto so as to improve the luminance of the output image by reflecting light initially directed inwards towards the photo-conductive of about l0lcm the intensity of light at the face away from the incident light may be less than 1 percent of what it is on the incident or input face. In addition, the impedance will be more than I00 times that of the incident face and this reduces the sensitivity accordingly.

In the Evans arrangement this loss is offset to some extent by optical feedback obtained by making the plates transparent so as to enable light generated in the EL layer and emitted back towards the photo-conductor to provide optical feed-back to take place and thus maintain the EL layer in a state of illumination. However, this restricts the use of the Evans panel to the display of static or substantially static images: moving images cannot be displayed in a practical manner by a system relying on optical feed-back as the image would be held static by this mechanism of generation.

The present invention provides a photo-conductive image intensifier panel comprising:

a. a photo-conductive (PC) input layer having its input face exposed to incoming light and having an array of spaced apertures;

layer.

The input electrode may be in the form of a single mesh bywhich the PC layer is subdivided into an array of separated elements each containing an input end of a coupling conductor. Preferably, however, the input electrode lies against the input face of the PC layer which layer is continuous except for the aforesaid apertures.

An embodiment of the invention incorporating the above preferred features willnow be described by way of example, with reference to the drawings accompanying the Provisional Specification in which:

FIG. 1 shows in fragmentary axial section a construction as described by Evans;

FIG. 2 shows in similar section a construction according to the present invention;

FIG. 3 shows a variant of the arrangement of FIG. 2;

FIGS. 4 and 5 are views illustrating one method of manufacture given by way of example.

Referring now to FIG. 1, the Evans construction is shown comprising a continuous photo-conductive (PC) input layer having its input face exposed to incoming light and a square-mesh input electrode El located against the output face of the said PC layer. Within each mesh of said input electrode there is a coupling conductor CC which is insulated except for having its input end in contact with an area of the output face of the PC layer. A conductive plate E2 is electrically connected to the output end of each of said coupling con ductors, all said plates being co-planar and spaced from each other so as form a regular array. The electroluminescent layer EL is in contact with the output faces of all of said plates, and an output electrode E3 is provided on the output face of the EL layer. In addition a filler F is provided and both said filler and the plates E2 are made transparent to allow optical feedback as explained above. Suitable A.C. excitation is provided between E1 and E3 from a source G.

In FIG. 2 corresponding parts have the same reference numerals. As will be seen, one essential difference is that the input electrode E1 is on the input face of the PC layer, and the PC layer has apertures for the coupling conductors CC to extend through. In addition (and as is preferred) these ends of the coupling conductors (also referred to hereinafter as pillars) are provided with flanges Cf to provide area contact (as opposed to mere edge contact) with the input face of the PC layer.

A further difference lies in the fact that the plates E2 (also referred to hereinafter as mosaic electrodes) and/or the filler F are opaque to light from the EL layer in order to prevent optical feedback as aforesaid.

Preferably the plates E2 are also made reflective to light from the EL layer so as to increase the image brightness.

As has been explained, it is important for the performance of the device that there should be good electrical contact between the grid El and pillars CC and the input face (as opposed to the output face) of the photo-conductive layer. This can be achieved or enhanced by making the grid E1 and/or the flanges Cf transparent to the radiation which is to be imaged. This can be understood by considering that any element of the photo-conductive layer which is deprived of input light will have a high resistance and will therefore constitute a bad connection to other areas of the photoconductive layer which are being irradiated. Thus if the grid E1 and/or flanges Cf are opaque to such radiation then said grid and flanges will have surface or area contact (in the plane of the device) with highly resistive parts of the photo-conductive layer and will only have edge contact (of small area) with the irradiated (and therefore more conductive) parts of thelayer. However if, as is preferred, the said grid E1 and flanges are made transparent, they will have not only the edge contact mentioned above, but they will also have larger area surface contact with underlying parts of the photo-conductive layer which are rendered conductive by input light passed by the grid and flanges themselves.

The PC layer may be relatively thin as shown in FIG. 2 in which case a further thicker layer F of a filling material is provided between the pillars CC. Alternatively, the whole of the space between the grid El and the electrodes E2 can be filled by the photo-conductor in which case, of course, nearly all the photo-conductor is acting as a mere filler and only a very thin layer at the input face is operative (in either event, the pillars are made to extend to the output face of the tiller so as to contact the plates E2). Such an arrangement is shown in FIG. 3.

The operative elements of the device are those illustrated in FIG. 2 and FIG. 3 which drawings are schematic particularly in two respects. First, the rigid substrate means required in practice to support the various layers is not shown. Secondly, the length of the pillars is shown much greater than it needs to be in practice, this v being done for ease of illustration. It is possible to form the various layers and electrodes on a single transparent substrate plate which may be either on the input side or on the output side. However, one method of manufacture will now be described as applied to a case in which two transparent plates are used (one on the input-side and one on the output side), some of the operative layers being provided on each plate before the two sections are joined together.

A first or input substrate is provided in the form of a relatively thick transparent plate W1 of glass (see FIG. 4) and on the output face of said plate are deposited, by conventional means, the grid pattern El and an array of discs which will form the flanges Cf. As the next step, the central parts of the flanges are plated up so as to form the pillars CC (these will be much shorter than shown in FIGS. 2 3 for practical convenience as aforesaid).

After the grid and pillars have been formed, the photo-conductive (PC) layer (not shown in FIG. 4) is deposited on the grid E1 and around the pillars and the said layer is then sintered. The photo-conductive layer may by a relatively thin layer as shown in FIG. 2 in which case a further thicker layer of a filling material is deposited between the columns. Alternatively, the whole of the space between the grid E1 and the electrodes E2 can be filled by photo-conductor as aforesaid. In either event, the pillars are made to extend to the output face of the filler and this can be done by wiping or grinding the output surface of the input section after sintering.

As the next step, a second substrate or output plate W2 (which may also be a relatively thick glass plate) is taken and provided with a transparent tin-oxide layer on its input face forming the electrode E3.

Subsequently the electroluminescent layer EL is provided on the tin-oxide with a suitable binder.

Next, a continuous conductive layer is provided by evaporation on the input face of the electroluminescent layer. A mosaic resist pattern is formed thereon and unwanted conductor is then etched away so as to leave the desired mosaic of square or substantially square mosaic electrodes E2.

The two sections of the device whichhave thus been formed are then brought together (see FIG. 5) under pressure after coating the interface with a liquid binder. The pressure applied forces the binder away from the points where the pillars protrude from the filler to contact the electrodes E2. This process can be monitored by applying suitable voltages to the device while the pressure is being applied. In this way, areas of the array where good contact between pillars and E2 electrodes has been achieved will be shown up by brighter light output from the electro-luminescent layer, and pressure on plates Wl W2 can be increased until the brightness of the display is uniform thus indicating that all pillars have contacted all the E2 electrodes. This process is assisted by the fact that the pillars are made of a soft material such as gold which can be deformed locally so as to take up irregularities in the two mating sections.

Although there are references herein to the plane" of the device and to elements being co-planar, it will be appreciated that the device can be slightly curved if desired. As for the references to light, the term should be read as including invisible light such as ultraviolet or infra-red.

Although separate plates or mosaic electrodes E2 have been shown in the drawings and although flanges Cf can be provided on separate plates, both kinds of elements (E2 and Cf) can be made integral with the pillars CC if the method of manufacture permits.

What we claim is:

1. A photo-conductive image intensifier panel comprising:

a. a photo-conductive input layer having an input face and an output face and having its input face adapted for exposure to incoming light and having an array of spaced apertures;

b. a plurality of input electrodes in contact with the input face of said photo-conductive layer at areas separated from said spaced apertures;

c. a plurality of coupling conductors having an input end and an output end and each disposed in a spaced aperture of the photo-conductive layer, each of said coupling conductors having its input end located within the aperture and at least in electrical contact with the input face of said photoconductive layer at the periphery of the aperture;

d. a conductive plate having an input face and an output face, said input face thereof being electrically connected to the output end of each of the said coupling conductors, all of said plates being co-planar and spaced from each other;

e. an electroluminescent layer in electrical contact with the output faces of all of said conductive plates;

f. a transparent output electrode having a surface in contact with the output face of said electroluminescent layer; and

g. means for maintaining said conductive plates opaque to light emitted by said electroluminescent layer whereby said coupling conductors electrically couple the photoconductive input layer to the electro-luminescent layer to increase the sensitivity and performance of said panel.

2. A panel as claimed in claim 1 wherein the said conductive plates reflect light from the EL layer in addition to being opaque thereto so as to improve the luminance of the output image.

3. A panel as claimed in claim 1 wherein the input electrode lies against the input face of the photo-com ductive layer which layer is continuous except for the said apertures.

4. A panel as claimed in claim 1 wherein the input ends of the coupling conductors are provided i with flanges to provide area contact with the input face of the photo-conductive layer.

5. A panel as claimed in claim 1 wherein the input electrode grid is transparent to the radiation which is to be imaged.

6. A panel as claimed in claim 1 wherein the whole of the space between said input electrode grid and the plates is filled by the photo-conductor, nearly all the photo-conductor acting as a mere filler and only a very thin layer thereof being operative at the input face.

7. A panel as claimed in claim 4, wherein the input electrode grid and said flanges are transparent to the radiation which is to be imaged.

8. A panel as claimed in claim ll, wherein said means is a filler disposed as a backing on said electroluminescent layer. 

2. A panel as claimed in claim 1 wherein the said conductive plates reflect light from the EL layer in addition to being opaque thereto so as to improve the luminance of the output image.
 3. A panel as claimed in claim 1 wherein the input electrode lies against the input face of the photo-conductive layer which layer is continuous except for the said apertures.
 4. A panel as claimed in claim 1 wherein the input ends of the coupling conductors are provided with flanges to provide area contact with the input face of the photo-conductive layer.
 5. A panel as claimed in claim 1 wherein the input electrode grid is transparent to the radiation which is to be imaged.
 6. A panel as claimed in claim 1 wherein the whole of the space between said input electrode grid and the plates is filled by the photo-conductor, nearly all the photo-conductor acting as a mere filler and only a very thin layer thereof being operative at the input face.
 7. A panel as claimed in claim 4, wherein the input electrode grid and said flanges are transparent to the radiation which is to be imaged.
 8. A panel as claimed in claim 1, wherein said means is a filler disposed as a backing on said electroluminescent layer. 